Exemplary embodiments of the invention relate to an internal combustion engine for a motor vehicle and a method for operating such an internal combustion engine.
German patent document DE 199 11 023 C2 discloses a direct-injection gasoline internal combustion engine having a combustion chamber delimited by a wall of the internal combustion engine, and having an injector associated with the combustion chamber. The injector is used for introducing fuel into the combustion chamber, and is at least partially accommodated in a receiving opening. The receiving opening is delimited by a wall area of the wall extending at least essentially parallel to the axial direction of the injector. The injector has at least one injection opening that opens into the combustion chamber via the receiving opening. This means that the fuel for operating the internal combustion engine may be introduced, in particular injected, into the combustion chamber via the injection opening in the injector and the receiving opening in the wall.
The injector is situated at least essentially in the center of the combustion chamber, and may inject the fuel into the combustion chamber with an at least essentially conical fuel jet or fuel spray. The injector itself is situated in the combustion chamber ceiling in such a way that due to the injection, an ignitable air-fuel mixture accumulates at a certain distance from a spark plug. This involves a spray-guided combustion process.
Internal combustion engines are known from European patent document EP 1 548 248 A2 and German patent document DE 697 12 155 T2, which have at least one combustion chamber delimited by at least one wall of the internal combustion engine and at least one injector which is associated with the combustion chamber. The particular injector is at least partially accommodated in a receiving opening. The receiving opening is delimited by a first wall area extending at least essentially parallel to the axial direction of the injector. The injector has at least one injection opening that opens into the combustion chamber via the receiving opening. In the direction of the combustion chamber, the first wall area is directly adjoined by a further wall area of the wall extending at an angle to the axial direction. The further wall area delimits an area of the receiving opening that expands at least essentially conically toward the combustion chamber. In addition, an at least essentially conical injection jet for introducing fuel for the internal combustion engine into the combustion chamber is achievable by means of the injector.
It has been shown that, especially for particularly small quantities of fuel injected by means of the injector, problems may result regarding the ignition stability and combustion stability, in particular in so-called stratified charge operation of the internal combustion engine.
Exemplary embodiments of the invention are directed to an internal combustion engine as well as a method for operating such an internal combustion engine of the type mentioned at the outset in such a way that particularly high combustion stability is achievable.
A first aspect of the invention relates to an internal combustion engine, in particular for a motor vehicle and in particular for a passenger vehicle. The internal combustion engine includes at least one combustion chamber, for example a cylinder, which is delimited by at least one wall of the internal combustion engine. In addition, the internal combustion engine includes at least one injector associated with the combustion chamber and which is at least partially accommodated in a receiving opening. The receiving opening is delimited by a first wall area of the wall extending at least essentially parallel to the axial direction of the injector. The receiving opening is designed, for example, as an at least essentially circular cylinder or straight circular cylinder, or is delimited in this form by the first wall area.
The injector has at least one injection opening that opens into the combustion chamber via the receiving opening. Fuel, in particular liquid fuel, for the internal combustion engine may thus be introduced, in particular injected and in particular directly injected, into the combustion chamber via the injection opening and the receiving opening.
In the direction of the combustion chamber, the first wall area is directly adjoined by a further wall area of the wall extending at an angle to the axial direction of the injector. The further wall area delimits an area of the receiving opening that expands at least essentially conically toward the combustion chamber. In addition, an at least essentially conical injection jet for introducing fuel for the internal combustion engine into the combustion chamber is achievable by means of the injector.
According to the invention, over its length relative to the radial direction of the injector, the further wall area is situated at a distance from the injector and in alignment with the injector, at least in places. In addition, the further wall area has a cone opening angle in a range of 50° up to and including 90°, the cone opening angle being smaller than a jet angle of the injection jet. The jet angle characterizes a cone opening angle of the at least essentially conical injection jet, and is referred to as the jet angle in order to satisfactorily conceptually differentiate it from the cone opening angle of the further wall area.
As a result of the cone opening angle of the further wall area being smaller than the jet angle of the injection jet, a mixture cloud composed of the injected fuel and the air supplied to the combustion chamber and which results from the injection of in particular liquid fuel, brought about by means of the injector, may be stabilized at the further wall area, and thus at the combustion chamber ceiling of the combustion chamber. In other words, due to this configuration of the further wall area, a convergent design of the surroundings of the injector in the combustion chamber is provided, so that the mixture cloud may be stabilized. A particularly advantageous and stable association and supply of the mixture cloud, for example at a spark plug associated with the combustion chamber, may thus be achieved, so that the mixture cloud, i.e., the mixture of the fuel and air, may be ignited very well by means of the spark and stably combusted. In this way the risk of misfires, in which the desired combustion of the air-fuel mixture in the combustion chamber does not occur, may also be kept particularly low.
Due to the appropriately configured receiving opening, a particularly ignitable air-fuel mixture and a particularly large quantity of the particularly ignitable air-fuel mixture reaches the spark plug. This is the case due to the fact that the mixture cloud may propagate particularly advantageously in the combustion chamber in a directionally stable manner.
The high combustion stability thus provided is particularly advantageous for the so-called stratified charge operation of the internal combustion engine, which may be carried out by means of the injector. Such stratified charge operation, in particular in the internal combustion engine designed as a gasoline engine, allows operation that is very low in emissions and fuel consumption, but imposes certain requirements in order to achieve stable combustion of the air-fuel mixture. These requirements may be met particularly well in the internal combustion engine according to the invention.
In stratified charge operation, the fuel is introduced into the combustion chamber by means of the injector in, for example, two or three injections in very rapid succession shortly before the upper ignition point. Typically, the penetration behavior of the subsequent injection is influenced by the preceding injection due to the induced flow, and the supply of an ignitable mixture to the spark plug is reduced. Especially for particularly small second and third injection quantities, which are advantageous for low emission values, the ignition stability and combustion stability may thus be adversely affected.
This problem is at least reduced in the internal combustion engine according to the invention. The flow influence of the main injection (the preceding injection) on the air-fuel mixture for the subsequent injection with a comparatively smaller injection quantity of fuel is particularly low, so that the mixture cloud propagates in a directionally stable manner. By means of the internal combustion engine according to the invention, a particularly advantageous spray-guided combustion process is thus provided, in which high combustion stability with only a low likelihood of misfires in the stratified charge operation of the gasoline engine with direct injection, and with an outwardly or inwardly injector in conjunction with injection times, is achievable for providing particularly low emissions.
In another advantageous embodiment of the invention, the further wall area extends over a length, relative to the axial direction of the injector, which is in a range of 3 mm up to and including 6 mm. Particularly advantageous flow conditions are thus achievable that result in particularly high combustion stability, and thus, a low likelihood of misfires.
It has been shown to be particularly advantageous when the first wall area rests at least indirectly against the injector. The injector is thus accommodated and held in the receiving opening in a particularly defined manner, and is not able to undesirably move relative to the wall, even at very high injection pressures.
Another embodiment is characterized in that a minimum distance between the further wall area and the injection jet which may be brought about by means of the injector when fuel is injected into the combustion chamber is in a range of 1 mm up to and including 4 mm. The propagation behavior of the injection jet and of the resulting air-fuel mixture is thus stabilized, resulting in particularly high combustion stability and a low likelihood of misfires.
In another embodiment of the invention, the internal combustion engine is designed as a gasoline engine. In particular for gasoline engines, stabilizing the mixture cloud plays an important role in enabling large quantities of ignitable mixture to be led to the spark plug, and consequently, achieving efficient, low-emission operation and keeping the risk of misfires low.
In another embodiment of the invention, stratified charge operation and/or homogeneous operation of the internal combustion engine may be carried out by means of the injector. The emissions as well as the fuel consumption of the internal combustion engine may thus be kept particularly low.
It has been shown to be particularly advantageous when a lateral surface of the injector on the outer peripheral side, which is designed at least essentially in the form of a straight circular cylinder, and the first wall area facing the combustion chamber end at the same height. In other words, the first wall area and the lateral surface of the injector on the outer peripheral side extend toward the combustion chamber to the same height. This results in particularly advantageous environmental conditions, so that the mixture cloud resulting from the injection of the fuel may be stabilized very well.
In another embodiment of the invention, the injector is designed as an outwardly opening or inwardly opening injector. Particularly high combustion stability may be achieved in this way.
Lastly, it has shown to be particularly advantageous when the further wall area is rotationally symmetrical with respect to a center axis of the injector. The wall area may thus be produced in a time- and cost-effective manner.
The injector is advantageously situated at least essentially centrally with respect to the combustion chamber. In other words, the center axis of the injector and a center axis of the combustion chamber coincide. This means that the center axes are in alignment.
A second aspect of the invention relates to a method for operating an internal combustion engine, in particular an internal combustion engine according to the invention. The internal combustion engine has at least one combustion chamber delimited by at least one wall of the internal combustion engine, and at least one injector which is associated with the combustion chamber and which is at least partially accommodated in a receiving opening which is delimited by a wall area of the wall which extends at least essentially parallel to the axial direction of the injector.
The injector has at least one injection opening which opens into the combustion chamber via the receiving opening, in the direction of the combustion chamber the first wall area being directly adjoined by a further wall area of the wall extending at an angle to the axial direction. An at least essentially conical area of the receiving opening that expands toward the combustion chamber is delimited by the further wall area.
Within the scope of the method, the injector brings about an at least essentially conical injection jet for introducing fuel for the internal combustion engine into the combustion chamber.
For achieving particularly high combustion stability, it is provided according to the invention that over its length relative to the radial direction of the injector, the further wall area is situated at a distance from the injector and in alignment with the injector, at least in places, and has a cone opening angle in a range of 50° up to and including 90°, the cone opening angle being smaller than a jet angle of the injection jet, and the internal combustion engine being operated in a stratified charge operation by means of the injector. Advantageous embodiments of the first aspect of the invention are considered as advantageous embodiments of the second aspect of the invention, and vice versa.
In stratified charge operation, which is typically also referred to as a stratified combustion process, high charge movements may result. Customarily, these high charge movements may have an adverse effect on the combustion stability. Due to the appropriate configuration of the combustion chamber, these charge movements may now be kept low, so that a mixture cloud composed of fuel and air may stably propagate in the combustion chamber and be led to a spark plug, for example, by means of which the mixture cloud may then be ignited.
If the internal combustion engine is a so-called supercharged internal combustion engine, which has at least one exhaust gas turbocharger for supplying the internal combustion engine with compressed air, this supercharging of the internal combustion engine typically results in very high charge movements. However, due to the configuration of the combustion chamber, a particularly robust stratified charge operation may be achieved, since the formation of an ignitable mixture at the spark plug may be ensured.
In addition, it is possible to operate the internal combustion engine at particularly high fuel pressures, for example in a range of 150 bar up to and including 300 bar, so that particularly efficient operation, and thus with low fuel consumption, is achievable.
The base area diameter of the at least essentially conical receiving opening is advantageously selected in such a way that the injection jet which may be brought about by means of the injector may propagate unhindered. In other words, it is provided that the second wall area does not hinder the propagation and formation of the injection jet.
Identical or functionally equivalent elements are provided with the same reference numerals in the figures.